let grade=[1,23,45,234,32];
console.log(Math.max.apply(null,grade));

console.log(Math.ceil(5.1));//向上取整，天花板
console.log(Math.floor(5.1));//向下取整，地板

console.log(5.678.toFixed(2));

Math.random();//0<= ~ <1任意数
//2-5
//min+Math.floor(Math.random()*(Max-Min+1))
console.log(2+Math.floor(Math.random()*(5-2+1)));